U.S. patent number 5,370,677 [Application Number 08/123,321] was granted by the patent office on 1994-12-06 for gamma matched, helical dipole microwave antenna with tubular-shaped capacitor.
This patent grant is currently assigned to Urologix, Inc.. Invention is credited to Stanley E. Kluge, Eric N. Rudie.
United States Patent |
5,370,677 |
Rudie , et al. |
December 6, 1994 |
**Please see images for:
( Certificate of Correction ) ** |
Gamma matched, helical dipole microwave antenna with tubular-shaped
capacitor
Abstract
A catheter shaft carries a coaxial cable, the terminal end of
which contains a dipole antenna with opposing first and second
helical elements. The first and second helical elements originate
from a common connection to an outer conductor of the coaxial
cable. The first and second helical elements are formed by winding
flat wire around an outer insulator of the coaxial cable near a
terminal end of the coaxial cable. A tubular-shaped capacitor is
connected between an inner conductor of the coaxial cable and a
point on the second helical element where the resistive component
of the antenna's impedance matches the characteristic impedance of
the coaxial cable. This match minimizes reflective losses of the
antenna, thereby maximizing power transfer to the antenna. The
antenna has an effective electrical length which is equal to one
half the wavelength of the radiation emitted, independent of the
physical length of the antenna. The antenna also has a radiation
length which can be adjusted by varying the number and pitch of
turns of the flat wire and the location of the impedance matching
point.
Inventors: |
Rudie; Eric N. (Maple Grove,
MN), Kluge; Stanley E. (Albertville, MN) |
Assignee: |
Urologix, Inc. (Minneapolis,
MN)
|
Family
ID: |
22407967 |
Appl.
No.: |
08/123,321 |
Filed: |
September 17, 1993 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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847915 |
Mar 6, 1992 |
5300099 |
|
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Current U.S.
Class: |
607/101; 606/41;
607/102; 607/116; 607/156 |
Current CPC
Class: |
A61B
18/18 (20130101); A61B 18/1815 (20130101); A61N
5/02 (20130101); A61N 5/045 (20130101); A61B
2018/00523 (20130101) |
Current International
Class: |
A61B
18/18 (20060101); A61N 5/02 (20060101); A61B
017/39 () |
Field of
Search: |
;606/41,42,45,48-50
;607/100,101,115,116,154-156,143 ;604/20,21 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Cheng, David K., Field and Wave Electromagnetics, pp. 112-113.
.
Hayt, William H., Jr., Engineering Electromagnetics, Fourth
Edition, pp. 161-163..
|
Primary Examiner: Pellegrino; Stephen C.
Assistant Examiner: Peffley; Michael
Attorney, Agent or Firm: Kinney & Lange
Parent Case Text
REFERENCE TO CO-PENDING APPLICATIONS
This application is a continuation-in-part of Ser. No. 07/847,915,
filed Mar. 6, 1992, now U.S. Pat. No. 5,300,099, entitled GAMMA
MATCHED, HELICAL DIPOLE MICROWAVE ANTENNA, by E. Rudie. Reference
is made to the following co-pending U.S. patent application Ser.
No. 07/847,718, filed Mar. 6, 1992, now U.S. Pat. No. 5,326,343,
entitled DEVICE FOR ASYMMETRICAL THERMAL THERAPY WITH HELICAL
DIPOLE MICROWAVE ANTENNA, by E. Rudie et al.; and Ser. No.
07/847,894, filed Mar. 6, 1992, now U.S. Pat. No. 5,330,518
entitled METHOD FOR TREATING INTERSTITIAL TISSUE ASSOCIATED WITH
MICROWAVE THERMAL THERAPY, by B. Neilson et al.
Claims
What is claimed is:
1. A device for microwave thermal therapy, the device
comprising:
a catheter;
a coaxial cable carried by the catheter having a first end, a
second end, an outer insulator, an outer conductor, an inner
insulator and an inner conductor;
a helical antenna having a first section and a second section
connected to the first section, the first and second sections being
of approximately equal length, a midpoint of the helical antenna
being electrically connected to the outer conductor; and
a tubular capacitor having an inner conductive layer, an outer
conductive layer and a dielectric layer between the inner
conductive layer and the outer conductive layer, the inner
conductive layer being electrically connected to the inner
conductor of the coaxial cable and the outer conductive layer being
electrically connected to the second section of the helical
antenna.
2. The device of claim 1 and further comprising adjustable
connector means associated with the outer conductive layer for
electrically connecting the outer conductive layer to the second
section of the helical antenna.
3. The device of claim 2 wherein the adjustable connector means is
positioned so as to define a connection point between the tubular
capacitor and the helical antenna which permits the tubular
capacitor to match an impedance between the helical antenna and the
coaxial cable.
4. The device of claim 1 and further comprising a conductive sleeve
which is positionable over and electrically connectable to the
outer conductive layer of the tubular capacitor.
5. The device of claim 4 wherein the conductive sleeve is connected
to the outer conductive layer of the tubular capacitor and the
helical antenna at a location which permits the tubular capacitor
to match an impedance between the helical antenna and the coaxial
cable.
6. The device of claim 1 and further including a tubular extension
having outer and inner dimensions approximating those of the outer
insulator of the coaxial cable, the tubular extension being
positioned over the outer conductor, the inner insulator and the
inner conductor at the second end of the coaxial cable, wherein the
helical antenna is positioned over the outer conductor of the
coaxial cable and the tubular extension, and wherein the tubular
capacitor is positioned within the tubular extension, the tubular
extension being configured to permit the helical antenna to be
connected to the outer conductor of the coaxial cable and the outer
conductive layer of the tubular capacitor.
7. The device of claim 1 wherein the tubular capacitor has a
capacitance of about 2.7 pF.
8. A device for thermal therapy, the device comprising:
a urethral catheter;
a coaxial cable carried by the catheter and being connectable to a
power source, the coaxial cable having an outer insulator, an outer
conductor, an inner insulator and an inner conductor;
a helical dipole antenna having a first location connected to the
outer conductor of the coaxial cable; and
a tubular capacitor having an inner conductive layer, an outer
conductive layer and a dielectric layer between the inner
conductive layer and the outer conductive layer, the inner
conductive layer being electrically connected to the inner
conductor of the coaxial cable and the outer conductive layer being
electrically connected to a second location of the helical
antenna.
9. The device of claim 8 and further comprising adjustable
connector means associated with the outer conductive layer for
electrically connecting the outer conductive layer to the second
location of the helical antenna.
10. The device of claim 9 wherein the adjustable connector means is
positioned so as to define a connection point between the tubular
capacitor and the helical antenna which permits the tubular
capacitor to match an impedance between the helical antenna and the
coaxial cable.
11. The device of claim 8 and further comprising a conductive
sleeve which is positionable over and electrically connectable to
the outer conductive layer of the tubular capacitor.
12. The device of claim 11 wherein the conductive sleeve is
connected to the outer conductive layer of the tubular capacitor
and the helical dipole antenna at a location which permits the
tubular capacitor to match an impedance between the helical dipole
antenna and the coaxial cable.
13. The device of claim 8 and further including a tubular extension
having outer and inner dimensions approximating those of the outer
insulator of the coaxial cable, the tubular extension being
positioned over the outer conductor, the inner insulator and the
inner conductor of the coaxial cable, wherein the helical dipole
antenna is positioned over the outer conductor of the coaxial cable
and the tubular extension, and wherein the tubular capacitor is
positioned within the tubular extension, the tubular extension
being configured to permit the helical dipole antenna to be
connected to the outer conductor of the coaxial cable and the outer
conductive layer of the tubular capacitor.
14. The device of claim 8 wherein the tubular capacitor has a
capacitance of about 2.7 pF.
15. A radiating device comprising:
a catheter;
a coaxial cable, carried by the catheter, having a first end, a
second end, an outer insulator, an outer conductor, an inner
insulator and an inner conductor:
an antenna having a first section and a second section connected to
the first section, the first and second sections being of
approximately equal length, a midpoint of the antenna being
electrically connected to the outer conductor;
a capacitor including a tubular-shaped dielectric having an outer
surface and an inner surface, a first conductive layer on the outer
surface and a second conductive layer on the inner surface;
an adjustable connector contacting the first conductive layer;
wherein the second conductive layer is connected to the inner
conductor of the coaxial cable, and wherein the adjustable
connector is connected to the antenna and the first conductive
layer at a point which allows the capacitor to match an impedance
of the coaxial cable and the antenna.
Description
BACKGROUND OF THE INVENTION
The present invention relates to the field of microwave thermal
therapy of tissue. In particular, the present invention relates to
an efficient microwave antenna for transurethral microwave thermal
therapy of benign prostatic hyperplasia (BPH).
The prostate gland is a complex, chestnut-shaped organ which
encircles the urethra immediately below the bladder. Nearly one
third of the prostate tissue anterior to the urethra consists of
fibromuscular tissue that is anatomically and functionally related
to the urethra and bladder. The remaining two thirds of the
prostate is generally posterior to the urethra and is comprised of
glandular tissue.
This relatively small organ, which is the most frequently diseased
of all internal organs, is the site of a common affliction among
older men: BPH (benign prostatic hyperplasia). BPH is a
nonmalignant, bilateral nodular expansion of prostrate tissue in
the transition zone, a periurethral region of the prostate between
the fibromuscular tissue and the glandular tissue. The degree of
nodular expansion within the transition zone tends to be greatest
anterior and lateral to the prostatic urethra, relative to the
posterior-most region of the urethra. Left untreated, BPH causes
obstruction of the urethra which usually results in increased
urinary frequency, urgency, incontinence, nocturia and slow or
interrupted urinary stream. BPH may also result in more severe
complications, such as urinary tract infection, acute urinary
retention, hydronephrosis and uraemia.
Traditionally, the most frequent treatment for BPH has been surgery
(transurethral resection). Surgery, however, is often not an
available method of treatment for a variety of reasons. First, due
to the advanced age of many patients with BPH, other health
problems, such as cardiovascular disease, can warrant against
surgical intervention. Second, potential complications associated
with transurethral surgery, such as hemorrhage, anesthetic
complications, urinary infection, dysuria, incontinence and
retrograde ejaculation, can adversely affect a patient's
willingness to undergo such a procedure.
A fairly recent alternative treatment method for BPH involves
microwave thermal therapy, in which microwave energy is employed to
elevate the temperature of tissue surrounding the prostatic urethra
above about 45.degree. C., thereby thermally damaging the tumorous
tissue, as well as adjacent healthy tissue. Delivery of microwave
energy to tumorous prostatic tissue is generally accomplished by a
microwave antenna-containing applicator, which is positioned within
a body cavity adjacent the prostate gland. The microwave antenna,
when energized, heats adjacent tissue due to molecular excitation.
The heat generated by the antenna is concentrated about the antenna
in a generally cylindrically symmetrical pattern which encompasses
and necroses tumorous, as well as healthy, intraprostatic tissue.
The necrosed intraprostatic tissue is subsequently resorbed by the
body, thereby relieving an individual from the symptoms of BPH.
This microwave treatment method is derived from a treatment for
prostatic cancer known as hyperthermia, in which microwave energy
is supplied by a microwave antenna to the prostate to elevate the
surrounding temperature to between about 43.degree. C.-45.degree.
C. Within this temperature range, healthy, well-vascularized tissue
is unharmed because of the circulatory system's ability to
effectively carry away the heat. Cancerous tissue, on the other
hand, has reduced vascularity, which restricts its ability to
adjust to the heat. Thus, heat concentrated in the region of the
cancerous tissue is sufficient to necrose the cancerous tissue, yet
insufficient to harm adjacent healthy tissue.
Microwave thermal therapy, because of its higher temperatures
(above about 45.degree. C.), provides the advantage of shortening a
treatment session's duration as compared to that of hyperthermia
with its lower temperatures (between about 43.degree. C. and
45.degree. C.). An undesirable consequence of microwave thermal
therapy, however, is the adverse effect the higher temperatures
have on healthy tissue adjacent the diseased area of the prostate.
The dilemma of selectively heating and necrosing only tumorous
prostatic tissue by microwave thermal therapy has been successfully
addressed in co-pending U.S. patent applications Ser. No.
07/847,718, now U.S. Pat. No. 5,326,343 entitled DEVICE FOR
ASYMMETRICAL THERMAL THERAPY WITH HELICAL DIPOLE MICROWAVE ANTENNA
and Ser. No. 07/847,894, now U.S. Pat. No. 5,330,518 entitled
METHOD FOR TREATING INTERSTITIAL TISSUE ASSOCIATED WITH MICROWAVE
THERMAL THERAPY.
Antennas which have been used for hyperthermia have a variety of
inadequacies which preclude their application to microwave thermal
therapy. First, such antennas often generate heat in two forms:
microwave energy and heat energy due to resistive losses of the
antenna. The efficiency of these antennas has not been of much
concern due to the relatively low amount of energy used to generate
interstitial temperatures of between about 43.degree. C. to
45.degree. C. and the lack of any adverse effect these temperatures
had on healthy tissue. Furthermore, it is known in the art that the
shape and size of a radiation pattern generated by some microwave
antennas are in part a function of how deeply the antenna is
inserted into the tissue. Prior microwave dipole antennas used for
hyperthermia have been unable to provide a predictable heating
pattern within tissue due to the variable effects caused by the
depth of insertion of the antennas into the tissue. Finally, the
radiation length of these antennas has not been easily variable to
accommodate the varying sizes of prostates requiring treatment. The
antenna designs of the prior art relating to hyperthermia,
therefore, have proven unsatisfactory for microwave thermal therapy
and its attendant higher temperatures.
The objective of microwave thermal therapy is to reduce the length
of a treatment session and to selectively heat and necrose only
undesirous tissue, while sparing, to the greatest extent possible,
adjacent healthy tissue. In order to avoid damage to tissues
immediately adjacent the microwave antenna-containing applicator
(i.e., the urethra, the ejaculatory duct and the rectum), it is
essential that the resistive losses of the antenna be reduced or
optimally eliminated. The ability to eliminate resistive losses and
utilize only microwave energy to heat a targeted tissue area would
permit a cooling system, such as that described in the co-pending
applications, to maintain safe temperatures adjacent to the
applicator by absorbing and carrying away any excess heat conducted
to the urethral tissues. In addition, the ability to construct an
antenna capable of producing a predictable, yet selectively
variable size heating pattern would aid in achieving an effective
treatment of undesirous tissue while minimizing harm to healthy
tissue.
SUMMARY OF THE INVENTION
The present invention is an improved helical antenna for thermal
treatment of interstitial tissues. The helical antenna is carried
by a coaxial cable which has an outer insulator, an outer
conductor, an inner insulator and an inner conductor. The coaxial
cable and antenna are in turn carried by a catheter. A midpoint of
the helical antenna is connected to the outer conductor of the
coaxial cable so as to form first and second helical sections of
approximate equal length. A tubular-shaped series capacitance
having an outer conductive layer, an inner conductive layer and a
dielectric layer therebetween is connected between the coaxial
cable and the helical antenna. The inner conductive layer of the
series capacitance is connected to the inner conductor of the
coaxial cable, while the outer conductive layer of the series
capacitance is connected to a point on the second helical section
where a resistive component of an impedance of the antenna matches
a characteristic impedance of the coaxial cable. This match
minimizes reflective losses of the antenna, thereby maximizing
power transfer to the antenna.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertical sectional view of a male pelvic region showing
the urinary organs affected by benign prostatic hyperplasia.
FIG. 2A is a side view of the distal end of the urethral catheter
of the present invention.
FIG. 2B is an enlarged sectional view of the proximal end of the
urethral catheter of the present invention.
FIG. 3 is a cross-sectional view of the urethral catheter of FIG.
2B taken along line 3--3.
FIG. 4 is a perspective view of a proximal region of the urethral
catheter with the end portion taken in section from line 4--4 of
FIG. 2B.
FIG. 5 is an enlarged view of the male pelvic region of FIG. 1
showing the urethral catheter of the present invention positioned
within the prostate region.
FIG. 6 is a graph illustrating temperature distribution generated
by the catheter of the present invention as a function of time.
FIG. 7 is a partial sectional view of the microwave antenna of the
urethral catheter of the present invention.
FIG. 8 is an exploded view of the microwave antenna shown in FIG.
7.
FIG. 9 is a block diagram of the transurethral microwave thermal
therapy system of the present invention.
FIG. 10A is an enlarged perspective view of a tubular-shaped
capacitor of an alternative embodiment of the present
invention.
FIG. 10B is a cross-sectional view of the tubular-shaped capacitor
of FIG. 10A taken along line 10B--10B.
FIG. 11 is a partial sectional view of the microwave antenna of the
present invention employing the tubular-shaped capacitor of FIG.
10A.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a vertical sectional view of a male pelvic region showing
the effect benign prostatic hyperplasia (BPH) has on urinary
organs. Urethra 10 is a duct leading from bladder 12, through
prostate 14 and out orifice 16 of penis end 18. Benign tumorous
tissue growth within prostate 14 around urethra 10 causes
constriction 20 of urethra 10, which interrupts the flow of urine
from bladder 12 to orifice 16. The tumorous tissue of prostate 14
which encroaches urethra 10 and causes constriction 20 can be
effectively removed by heating and necrosing the encroaching
tumorous tissue. Ideally, with the present invention, only
periurethral tumorous tissue of prostate 14 anterior and lateral to
urethra 10 is heated and necrosed to avoid unnecessary and
undesirous damage to urethra 10 and to adjacent healthy tissues,
such as ejaculatory duct 24 and rectum 26. Selective heating of
benign tumorous tissue of prostate 14 (transurethral thermal
therapy) is made possible by microwave antenna-containing catheter
28 of the present invention, which is shown in FIGS. 2A and 2B.
FIG. 2A shows a side view of a distal end of catheter 28, while
FIG. 2B shows an enlarged sectional view of a proximal end of
catheter 28. As shown in FIGS. 2A and 2B, catheter 28 generally
includes multi-port manifold 30, multi-lumen shaft 32, shaft
position retention balloon 34, connection manifold 35, cooling
system 36 and microwave generating source 38.
Manifold 30 includes inflation port 40, urine drainage port 42,
microwave antenna port 44, cooling fluid in port 46 and cooling
fluid out port 48. Ports 40-48 communicate with corresponding
lumens within shaft 32. Manifold 30 is preferably made of
medical-grade silicone sold by Dow Corning under the trademark
Silastic Q-7-4850.
Shaft 32 is connected to manifold 30 at shaft distal end 50. Shaft
32 is a multi-lumen, Foley-type urethral catheter shaft which is
extruded from a flexible, medical-grade silicone sold by Dow
Corning under the trademark Silastic Q-7-4850. Shaft 32, which has
an outer diameter of between about 16 French to 22 French, includes
outer surface 52, which is generally elliptical in cross-section as
shown in FIG. 3. Shaft 32 is long enough to permit insertion of
proximal shaft end 54 through urethra 10 and into bladder 12. In
one preferred embodiment, shaft 32 is coated with a hydrophilic
solution sold by Hydromer, Inc. under the mark Hydromer, which
lubricates outer surface 52 of shaft 32 and facilitates its
advancement within urethra 10.
As shown in FIGS. 2B, 3 and 4, shaft 32 includes temperature
sensing lumen 56, microwave antenna lumen 58, urine drainage lumen
60, balloon inflation lumen 62, cooling fluid intake lumens 64A and
64B, and cooling fluid exhaust lumens 66A and 66B. Lumens 56-66B
generally extend from distal shaft end 50 to proximal shaft end
54.
Temperature sensing lumen 56 is positioned near first side 68 of
shaft 32. Temperature sensing lumen 56 communicates with microwave
antenna port 44 and permits insertion of thermometry sensor 69
within shaft 32 to monitor temperature when shaft 32 is inserted
within urethra 10. Sensor 69 exits through port 44 and is connected
through connection manifold 35 to urethral thermometry unit 178B
(shown in FIG. 9). In a preferred embodiment, thermometry sensor 69
is a fiber optic luminescence type temperature sensor sold by
Luxtron Corporation. Temperature sensing lumen 56 is sealed at
proximal end 54 by silicone plug 70.
Microwave antenna lumen 58 is eccentric to the longitudinal axis of
shaft 32, antenna lumen 58 being positioned nearer first side 68 of
shaft 32 than second side 72 of shaft 32. Antenna lumen 58 is
sealed at proximal end 54 by silicone plug 70A. At its distal end,
antenna lumen 58 communicates with microwave antenna port 44.
Microwave antenna 74 is permanently positioned within antenna lumen
58 near balloon 34. Antenna 74 is positioned within antenna lumen
58 so as to be generally situated adjacent the benign tumorous
tissue of prostate 14 when shaft 32 is properly positioned within
urethra 10. As shown in FIGS. 2A-2B, antenna 74 is bonded within
antenna lumen 58 by adhesive bond 75. Antenna 74 is carried at the
proximal-most end of coaxial cable 76. The distal-most end of
coaxial cable 76 is connected to connection manifold 35 by a
conventional quick-coupling fitting 73. Coaxial cable 76
communicates with microwave generating source 38 by connection
cable 76A, which is connected between microwave generating source
38 and connection manifold 35. In one embodiment, connection cable
76A is a standard RG 400 coaxial cable. Microwave generating source
38 produces a maximum of 100 watts of electrical power at about 915
MHz frequency, +/- 13 MHz, which is within the FCC-ISM standards.
When antenna 74 is energized by microwave generating source 38,
antenna 74 emits electromagnetic energy which causes heating of
tissue within prostate 14.
Urine drainage lumen 60 is positioned adjacent antenna lumen 58,
between antenna lumen 58 and second side 72. Urine drainage lumen
60 communicates with urine drainage port 42 and defines a drainage
path for urine when proximal end 54 of shaft 32 is inserted within
bladder 12. Urine drainage lumen 60 is connected to urine drainage
lumen extension 78 at proximal end 54. Urine drainage lumen
extension 78 is bonded within proximal end cap 80. End cap 80 is
further bonded over outer surface 52 of shaft 32 at proximal shaft
end 54, with cavity 82 surrounding lumen extension 78. With end cap
80 and urine drainage lumen extension 78 in place, opening 84 to
lumen extension 78 permits urine to drain from bladder 12 through
urine drainage lumen 60 and out urine drainage port 42 when
proximal shaft end 54 is inserted within bladder 12. Drainage of
urine from bladder 12 is necessary due to frequent bladder spasms
which occur during transurethral thermal therapy.
Balloon inflation lumen 62 is positioned near second side 72,
generally between urine drainage lumen 60 and second side 72.
Balloon inflation lumen 62 communicates with inflation port 40 and
is sealed at proximal end 54 by silicone plug 70B. Balloon
inflation lumen 62 communicates with interior 86 of balloon 34 by
opening 88.
Balloon 34, which is formed from a tubular section of a flexible,
medical-grade silicone sold by Dow Corning under the trademark
Silastic Q-7-4720, is secured over shaft 32 by bonding balloon
waists 90 and 92 over exterior surface 52 of shaft 32 near proximal
shaft end 54. Balloon 34 is inflated by an inflation device 188
(shown in FIG. 9), which is connected to inflation port 40 and
which supplies positive fluid pressure to interior 86 of balloon
34. Balloon 34 is deflated when inflation device 188 supplies a
negative fluid pressure (i.e., a vacuum) to interior 86 of balloon
34. Balloon 34 serves to retain shaft 32 in a fixed position within
urethra 10 when balloon 34 is inflated within bladder 12 near
bladder neck 22, as shown in FIG. 5.
As shown in FIGS. 2B-4, cooling fluid intake lumens 64A, 64B are
positioned circumjacent first side 68, between first side 68 and
antenna lumen 58. Cooling fluid intake lumens 64A, 64B extend from
distal shaft end 50 to proximal shaft end 54 where lumens 64A, 64B
are exposed to cavity 82 of end cap 80. Intake lumens 64A, 64B are
relatively narrow in cross-section and have a relatively small
cross-sectional surface area. Water contained within intake lumens
64A, 64B performs two essential functions. First, water contained
within lumens 64A, 64B absorbs some of the microwave energy emitted
by antenna 74. This assists, in part, in controlling the volume of
tissue adjacent first side 68 of shaft 32 that is heated above
about 45.degree. C. Second, the water within lumens 64A, 64B
absorbs heat energy generated by the microwave energy from adjacent
tissues (i.e., urethra 10) via thermal conduction. This prevents
the portion of urethra 10 adjacent first side 68 from being
overheated and damaged when antenna 74 is energized.
Cooling fluid exhaust lumens 66A, 66B are circumjacent second side
72 with lumens 66A, 66B generally positioned between second side 72
and antenna lumen 58. Like intake lumens 64A, 64B, exhaust lumens
66A, 66B extend from shaft distal end 50 to shaft proximal end 54
where exhaust lumens 66A, 66B are exposed to cavity 82 of end cap
80. Exhaust lumens 66A, 66B are wider in cross-section than intake
lumens 64A, 64B, and have a cross-sectional area greater than the
cross-sectional area of intake lumens 64A, 64B. Water within
exhaust lumens 66A, 66B is therefore capable of absorbing a greater
amount of microwave energy when antenna 74 is energized. As a
result, for a given power output from microwave generating source
38, the temperature of tissue adjacent second side 72 will remain
below about 45.degree. C. Water within exhaust lumens 66A, 66B also
absorbs heat energy from adjacent tissue (i.e., urethra 10) when
antenna 74 is energized, which prevents the portion of urethra 10
adjacent second side 72 from being overheated and damaged when
antenna 74 is energized.
Intake lumens 64A, 64B and exhaust lumens 66A, 66B are supplied
with deionized water from cooling system 36. Water from cooling
system 36 is chilled to between about 12.degree.-15.degree. C. and
pumped at a rate of between about 100-150 milliliters per minute
via water feed line 94A to connection manifold 35. The water flows
through connection manifold 35 to water feed line 94B and to water
intake port 46, which communicates with water intake lumens 64A,
64B. Under fluid pressure, the water circulates through intake
lumens 64A, 64B to cavity 82 of end cap 80. The water returns to
cooling system 36 through exhaust lumens 66A, 66B to fluid exhaust
port 48. The water is carried from water exhaust port 48 via water
return line 96B to connection manifold 35, and from connection
manifold 35 to cooling system 36 via water return line 96A. The
water is then re-chilled and re-circulated. Water feed line 94B and
water return line 96B are each provided with a conventional
quick-coupling fitting 65A and 65B, respectively, which permits
catheter 28 to be easily disconnected from cooling system 36.
FIG. 5 shows an enlarged view of the male pelvic region of FIG. 1
with catheter 28 properly positioned within urethra 10. Orientation
stripe 98 along exterior surface 52 on first side 68, as shown in
FIG. 4, ensures the proper orientation of shaft 32 within urethra
10. As shown in FIG. 5, shaft 32 is positioned within urethra 10
with second side 72 of shaft 32 oriented toward rectum 26. Water
exhaust lumens 66A, 66B are oriented posteriorly, toward rectum 26
and water intake lumens 64A, 64B are oriented anteriorly toward
fibromuscular tissue 100 of prostate 14. The portion of transition
zone 101 anterior and lateral to urethra 10 is the most frequent
location of the tumorous tissue growth which causes BPH. Since
water exhaust lumens 66A, 66B are capable of absorbing more
microwave energy than water intake lumens 64A, 64B, the radiation
patterns created by microwave energy emitted from antenna 74 are
asymmetrical. Thus, a relatively large volume of tissue enveloping
the anterior portion of transition zone 101, adjacent first side
68, is heated to a temperature above about 45.degree. C., which
effectively necroses the tumorous tissue of prostate 14 which
encroaches upon urethra 10. In comparison, the temperature of
tissue adjacent second side 72 remains below about 45.degree. C.,
thereby eliminating the harmful effects of the microwave energy to
ejaculatory duct 24 and rectum 26.
FIG. 6 is a graph which generally demonstrates a microwave thermal
therapy procedure and a temperature distribution which was
generated by catheter 28 of the present invention, with shaft 32
inserted into a polyacrylamide gel formulation which simulates
biological tissue. The formulation and preparation procedures for
the polyacrylamide gel are discussed in detail in D. Andreuccetti,
M. Bini, A. Ignesti, R. Olmi, N. Rubino, and R. Vanni, Use of
Polyacrylamide as a Tissue-Equivalent Material in the Microwave
Range, 35 IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING 275 (NO. 4,
April 1988). FIG. 6 shows temperature measurements taken from eight
temperature sensors. Four sensors were aligned at fixed distances
adjacent first side 68. Sensor 1A was positioned immediately
adjacent shaft 32; sensor 1B was positioned about 0.66 cm from
shaft 32; sensor 1C was positioned about 1.33 cm from shaft 32; and
sensor 1D was positioned about 2.0 cm from shaft 32.
Four sensors were also aligned at fixed distances adjacent second
side 72. Sensor 2A was positioned immediately adjacent shaft 32;
sensor 2B was positioned about 0.66 cm from shaft 32; sensor 2C was
positioned about 1.33 cm from shaft 32; and sensor 2D was
positioned about 2.0 cm from shaft 32.
The x-axis represents a relative period of time over which the
microwave thermal therapy procedure was performed. The y-axis
represents temperature in degrees Celsius, with horizontal line H
representing 45.degree. C. (the temperature at or above which cells
are necrosed).
As generally shown in FIG. 6, the microwave thermal therapy
procedure of the present invention includes five operating phases,
P1-P5. Lines 1A-1D and 2A-2D correspond with sensors 1A-1D and
2A-2D, respectfully. During first phase P1, cooling system 36 is
turned on and chilled water is pumped through cooling lumens 64A,
64B and 66A, 66B. A drop in temperature immediately adjacent shaft
32 is represented by lines 1A, 2A. At the end of first phase P1,
cooling system 36 is turned off. At the beginning of second phase
P2, a relatively small amount of power (about 5 watts) is applied
to microwave antenna 74. The temperature immediately adjacent shaft
32 rises asymmetrically due to the greater absorptivity of water in
the larger exhaust lumens 66A, 66B on second side 72, as shown by
lines 1A, 2A. The power is applied long enough to merely warm
adjacent tissue to about 40.degree. C. By the end of second phase
P2, temperatures generally return to base line temperature.
In a preferred embodiment of the present invention, the tissue
responses to the chilling during P1 and the heating during P2 aid
in determining the vascularity of the tissue to be treated. This
information aids in determining the amount of power necessary to
treat tumorous tissue of prostate 14.
At the beginning of third phase P3, cooling system 36 is again
turned on thereby pumping chilled water through cooling lumens
64A-66B. The temperature immediately adjacent shaft 32
correspondingly drops as indicated by lines 1A, 2A. Prechilling of
the tissue immediately adjacent shaft 32 aids in protecting the
tissues immediately adjacent shaft 32 (i.e., urethra 10) from
overheating due to a relatively rapid application of power from
antenna 74.
Microwave generating source 38 is again turned on at the beginning
of fourth phase P4 at a sustained power output of about 20 watts.
As shown in FIG. 6, due to the absorptivity differential between
water in the narrower intake lumens 64A, 64B and water in the wider
exhaust lumens 66A, 66B, temperatures adjacent second side 72,
represented by lines 2A-2D, are cooler than temperatures adjacent
first side 68, represented by lines 1A-1D. The temperature
differentials are most profound within a target volume of tissue
0.66 cm from shaft 32. Within this target volume, as shown by lines
1A, 2A and 1B, 2B, the difference in temperature from first side 68
and second side 72 is on the order of about 10.degree. C. Thus, by
adjusting cooling system parameters or power output from microwave
generating source 38, tissue within 0.66 cm of first side 68 can be
heated to temperatures at or above about 45.degree. C., while
tissue within 0.66 cm of second side 72 can remain at temperatures
substantially below 45.degree. C. In this manner, tissue-necrosing
temperatures within the target volume are essentially restricted
only to tissue near first side 68, which is the most frequent
location of periurethral tumorous prostatic tissue. Alternatively,
by adjusting the power output or cooling system parameters, a
relatively small volume of tissue adjacent second side 72 can be
heated above about 45.degree. C. to necrose some of the tumorous
prostatic tissue which is posterior and lateral to the urethra. In
the preferred embodiment, during fourth phase P4, microwave
generating source 38 is operated for at least about 45 minutes.
As shown by lines 1A, 2A, during P4, the temperature of tissue
immediately adjacent shaft 32 (which is representative of
temperatures of urethra 10), as well as temperatures of tissue
beyond 0.66 cm from shaft 32, as shown by lines 1C, 2C and 1D, 2D,
are maintainable well below 45.degree. C. This is accomplished by
adjusting cooling system parameters and, if necessary, power output
from microwave generating source 38.
At the end of fourth phase P4 power is turned off. At the beginning
of fifth phase P5, cooling system 36 continues to operate,
circulating water through cooling lumens 64A-66B. A temperature
drop immediately adjacent shaft 32 is relatively rapid as shown by
lines 1A, 2A within P5. In a preferred embodiment of the present
invention, cooling system 36 continues to operate for a period of
time (on the order of 10 to 120 minutes) after the procedure to
cool urethra 10 and reduce edema resulting from the application of
heat to the periurethral tissues of prostate 14. In an alternative
embodiment, water feed line 94B, water return line 96B and
thermometry sensor 69 (as shown in FIG. 2A) are disconnected from
connection manifold 35. Water feed line 94B and water return line
96B of catheter 28 are then connected to another cooling system
similar to cooling system 36 and water is then circulated through
cooling lumens 64A-66B in a manner similar to that previously
described. In this fashion, recovery from the previously described
procedure can be accomplished away from the treatment area thereby
enabling microwave generating source 38 and cooling system 36 to be
readily available for treatment of another patient.
FIG. 7 shows a partial sectional view of microwave antenna 74 of
the present invention. Antenna 74 is positioned at a proximal-most
end of shielded coaxial cable 76. Cable 76 is a standard RG 178U
coaxial cable and includes inner conductor 120, inner insulator
122, outer conductor 124, and outer insulator 126. Outer insulator
126, outer conductor 124 and inner insulator 122 are stripped away
to expose about 3 millimeters of outer conductor 124, about 1
millimeter of inner insulator 122 and about 1 millimeter of inner
conductor 120. Capacitor 128 includes first end 130, which is
connected to inner conductor 120 by soldering, and second end 132,
which connects to antenna 74. Capacitor 128 serves to counteract a
reactive component of antenna 74, thereby providing a 50 ohm match
between coaxial cable 76 and microwave generating source 38, and
antenna 74.
Tubular extension 134, which is a hollow section of outer insulator
126 of coaxial cable 76, is positioned over capacitor 128 and the
exposed length of inner insulator 122 and secured by bond 136.
Tubular extension 134 includes hole 138, which provides an exit for
second end 132 of capacitor 128. Wound about outer insulator 126
and tubular extension 134 is flat wire 140. Flat wire 140 is a
single piece of flat copper wire with dimensions of about 0.009
inch by about 0.032 inch in cross-section, which provides a
relatively large surface area for maximum current flow while
minimizing the cross-sectional size of antenna 74.
FIG. 8 is an exploded view of a portion of antenna 74 which shows
its helical dipole construction. Generally, the efficiency of any
dipole antenna is greatest when the effective electrical length of
the antenna is generally one half the wavelength of the radiation
emitted in the surrounding medium. Accordingly, a relatively
efficient simple dipole antenna, operating at about 915 MHz, would
require a physical length of about 8 centimeters which, according
to the present invention, would needlessly irradiate and damage
healthy tissue. Furthermore, the physical length of a relatively
efficient simple dipole antenna operating at about 915 MHz cannot
be varied.
As shown in FIG. 8, flat wire 140 is soldered to outer conductor
124 at solder point 146. Flat wire 140 is then wound in a distal
direction about outer insulator 126 and in a proximal direction
about tubular extension 134, thereby forming first wire section 142
and second wire section 144, both of which are of equal length. In
one embodiment, first and second wire sections 142 and 144 are each
comprised of eight, equally-spaced windings of flat wire 140. The
combined length of first and second wire sections 142 and 144, and
hence the overall length of antenna 74, ranges from about 1.5
centimeters to about 4.0 centimeters, and varies according to the
length of the area of prostate 14 which requires treatment. A
standard medical-grade silicone tube (not shown), which has been
allowed to soak in a solvent, such as Freon, is positioned over
first and second wire sections 142 and 144. As the solvent
evaporates, the silicone tube shrinks, thereby securing flat wire
140 to outer insulator 126 and tubular extension 134.
The helical dipole construction of the present invention allows
antenna 74 to range in physical length from about 1.5 to 4
centimeters, while electrically behaving like an eight
centimeter-long simple dipole antenna. In other words, antenna 74
has an effective electrical length generally equal to one half of
the wavelength of the radiation emitted in the surrounding medium,
independent of its physical length. For purposes of definition, the
surrounding medium includes the catheter shaft and the surrounding
tissue. This is accomplished by varying the number and pitch of the
windings of first and second wire sections 142 and 144. A family of
catheters, which contain relatively efficient helical dipole
antennas of different physical lengths, permits selection of the
antenna best suited for the particular treatment area. In addition,
antenna 74 of the present invention is capable of producing a
constant heating pattern in tissue, concentrated about antenna 74,
independent of the depth of insertion into the tissue.
Second end 132 of capacitor 128, which exits hole 138, is soldered
to second wire section 144 at tap point 148, as shown in FIG. 7.
Tap point 148 is a point at which the resistive component of the
combined impedance of first wire section 142 and second wire
section 144 matches the characteristic impedance of coaxial cable
76. The impedance of either first wire section 142 or second wire
section 144 is expressed as Z, where Z=R +jX. The impedance Z
varies from a low value at solder point 146 to a high value at a
point farthest from solder point 146. There exists a tap position
where R is equal to 50 ohms, but an imaginary component, X, is
inductive. This inductive component can be canceled by inserting a
series capacitance, such as capacitor 128, which has a value of -jX
ohms. This results in an impedance match of 50 ohms real. The
resulting method of feeding antenna 74 is commonly called gamma
matching. In one embodiment of the present invention, where the
physical length of flat wire 140 is about 2.8 cm, tap point 148 is
about 3.5 turns from solder point 146 on second wire section 144.
In the preferred embodiment, the value of capacitor 128 is about
2.7 pF. However, as is known in the art, for other frequencies of
operation, appropriate values of capacitor 128 can be easily
determined.
The helical dipole construction of antenna 74 achieves a relatively
small size, which permits intraurethral application. The helical
dipole construction is also responsible for three features which
enable antenna 74 to achieve greater efficiency than prior known
interstitial microwave antennas: good impedance matching, good
current carrying capability and an effective electrical length
which is generally one half of the wavelength of the radiation
emitted in the surrounding medium, independent of the physical
length of antenna 74.
First, the good impedance match between antenna 74 and inner
conductor 120 minimizes reflective losses of antenna 74, with
measured reflective losses of less than 1% in a preferred
embodiment. Second, the use of flat ribbon wire 140 for first wire
section 142 and second wire section 144 minimizes resistive losses
of antenna 74 by providing a greater surface area upon which RF
current can be carried. Finally, the helical dipole design of
antenna 74 has an effective electrical length which is generally
one half of the wavelength of the radiation emitted in the
surrounding medium, independent of the physical length of antenna
74. This permits the physical length of antenna 74 to be varied to
accommodate varying sizes of individual prostates while maintaining
the same efficient, effective electrical length of antenna 74.
The use of an efficient microwave antenna is critical to the
ability to focus thermal energy a distance from the antenna within
a target volume. An inefficient antenna produces a lesser intensity
of microwave radiation within the target volume than desired. It
also produces undesired heat close to the urethra, which will
damage the urethra if not carried away by an increased coolant
flow. This added burden on the cooling system reduces its capacity
to protect the urethra, thereby limiting the microwave power that
can be radiated without elevating urethra temperatures above safety
limits. With microwave power limited by cooling system capacity,
the heat delivered to the desired target area of the prostate will
not be sufficient for effective therapy. The efficient helical
dipole design of antenna 74 of the present invention, however,
ensures that almost all heat delivered during the treatment is
delivered in the form of microwave energy, rather than conductive
heat energy.
FIG. 9 is a block diagram of transurethral microwave thermal
therapy system 170, with which urethral catheter 28 is used. System
170 includes cooling system 36 microwave generating source 38, user
interface 172, real time controller (RTC) 174, directional coupler
176, thermometry sensors 182 and 184, coolant pressure sensor 186,
balloon inflation device 188, and urine collection container
190.
As shown in FIG. 9, control of microwave generating source 38 and
cooling system 36 is effected by real time controller 174, which is
in turn controlled by user interface 172. User interface 172 is an
IBM compatible machine containing two hard drives for data storage:
one for backup, and one for normal operation of system 170. User
interface 172 communicates with RTC 174, which is responsible for
all closed loop feedback to run system 170. RTC 174 has direct
closed loop control of microwave power from microwave generating
source 38, and coolant flow and coolant temperature of cooling
system 36. Closed loop feedback tracks out variations in gain,
drift and cable losses inherent in microwave generating source 38,
and variability in pump output and refrigeration system efficiency
of cooling system 36. In addition to monitoring microwave
generating source 38 and cooling system 36, RTC 174 also monitors
and controls several channels of thermometry via inputs from
thermometry unit 178. Cooling system thermometry 178A measures the
coolant and chiller temperatures based upon signals from coolant
temperature sensors 182 and 184 and a chiller temperature sensor
(not shown) of cooling system 36. Urethral thermometry 178B
measures urethral temperature based upon signals from temperature
sensor 69 within catheter 28. Rectal thermometry 178C measures
rectal temperature based upon signals received from a sensor (not
shown) within rectal probe 180.
RTC 174 transmits all closed-loop feedback to user interface 172,
which processes the input and transmits corrections and
instructions back to RTC 174. RTC 174 interprets the instructions
given to it by process control language received from user
interface 172 and executes the instructions in real time. All
corrections from user interface 172 are made to maintain a given
thermal profile throughout the transurethral thermal therapy. In
addition, system 170 includes a hardware fail-safe circuit which
shuts down system 170 should any parameter fall outside a given
range of values.
FIGS. 10A, 10B and 11 show a tubular-shaped capacitor 200 used in
another embodiment of antenna 214. Antenna 214 is constructed in a
manner similar to antenna 76, which is shown in FIGS. 7 and 8. As
shown in FIGS. 10A-10B, capacitor 200 comprises dielectric tube 202
with outer conductive layer 204 and inner conductive layer 206.
Outer conductive layer 204 and inner conductive layer 206 form
concentric plates of capacitor 200. Metal ring 208, which includes
tab 210, fits over outer conductive layer 204. Ring 208 is
positionable along capacitor 200 so as to locate tab 210 at the
desired tap point, similar to tap point 148 of FIG. 7, when
capacitor 200 is connected to antenna 214 (shown in FIG. 11).
Thereafter, ring 208 is soldered to outer conductive layer 204 of
capacitor 200.
In one preferred embodiment, capacitor 200 is manufactured by Coors
Ceramics Co. of Golden, Colo., with dielectric tube 202 being
formed from alumina, and with the inner conductive layer 206 and
outer conductive layer 204 being formed by application of a layer
of a metal-laced adhesive binder. Ring 208 and tab 210 are
preferably formed from any solderable metal, such as brass or
copper. Capacitor 200 has an outer diameter of about 0.050 inches,
which permits capacitor 200 to fit within a relatively flexible
tubular extension 216 (shown in FIG. 11). In addition, capacitor
200 has an inner diameter of about 0.025 inches, which permits
insertion of inner conductor 218 of coaxial cable 220 (shown in
FIG. 11) into capacitor 200. Like capacitor 128 of FIG. 7,
capacitor 200 has a capacitance of about 2.7 pF. Capacitor 200 also
has a length of about 0.110 inches. Other dimensions of capacitor
200 will be apparent to those of ordinary electrical skill.
FIG. 11 is a side view of antenna 214 with a portion cut away to
show a connection of capacitor 200 to antenna 214 and coaxial cable
220. Antenna 214 is connected to coaxial cable 220 in a manner
similar to that previously discussed with respect to antenna 74 and
coaxial cable 76 (FIG. 7). As shown in FIG. 11, metal band 222
(which is similar to ring 208) is positioned over inner insulator
223 and outer conductor 224 and connected by soldering to outer
conductor 224 of coaxial cable 220. Metal band 222 includes tab
226, which is connected by soldering to flat wire 228 so as to
produce first antenna section 214A and second antenna section 214B.
Like first and second wire sections 142 and 144 of antenna 74
(shown in FIG. 8), first antenna section 214A and second antenna
section 214B are approximately equal in length. Metal band 222 is
sized to be located within tubular extension 216 when tubular
extension 216 is positioned over inner insulator 223 and outer
conductor 224. A groove in tubular extension 216 (not shown)
enables the connection of tab 226 of metal band 222 to flat wire
228.
Prior to the positioning of tubular extension 216, capacitor 200 is
slipped over inner conductor 218. Inner conductive layer 206 of
capacitor 200 is thereafter connected to inner conductor 218 by
soldering. Capacitor 200 is preferably spaced apart from outer
conductor 224 by at least about 0.050 inches to avoid a short
between outer conductor 224 and outer conductive layer 204 of
capacitor 200. With capacitor 200 connected to inner conductor 218,
the relatively flexible tubular extension 216 is slipped over
capacitor 200, ring 208, inner insulator 223 and outer conductor
224 until tab 210 of ring 208 engages hole 230 of tubular extension
216. Hole 230 is located so as to expose tab 210 for soldering to
second antenna section 214B at tap point 232. Tap point 232, like
tap point 148 of FIG. 7, is the point at which the resistive
component of the combined impedance of first antenna section 214A
and second antenna section 214B matches the characteristic
impedance of coaxial cable 220.
The tubular shape of capacitor 200 provides for a highly reliable
connection to inner conductor 218 and tap point 232. In addition,
capacitor 200 permits adjustment of tap point 232 by virtue of the
adjustability of ring 208. Thus, capacitor 200 is able to be
adapted for use with various antenna dimensions.
Although the present invention has been described with reference to
preferred embodiments, workers skilled in the art will recognize
that changes may be made in form and detail without departing from
the spirit and scope of the invention. For example, while the
beneficial uses of the microwave antenna-containing catheter of the
present invention have been described with respect to the urethra,
other intracavitary applications are implied.
* * * * *